Motor vehicles may provide steering assistance to amplify a force or torque applied by a driver of the vehicle (i.e., at a steering wheel) to the steering assembly of the vehicle. Vehicles, for example, generally have either electric power assisted steering (EPAS) or hydraulic power steering. Hydraulic power steering, for example, relies on pistons in the steering rack with pressurized fluid to provide steering assistance, while EPAS does away with the hydraulic pistons and instead uses a simple motor to help push the steering rack as the driver turns the steering wheel.
Vehicles with power steering systems may also be equipped with adaptive steering systems, such as, for example, adaptive front steering (AFS) systems. Adaptive steering systems may, for example, continuously and intelligently alter the relationship between a driver's steering inputs at the steering wheel and the angle of the steered road wheels of the vehicle. An adaptive steering system, for example, varies the degree that the road wheels turn in response to rotation of the steering wheel via a mechatronic auxiliary system. At lower speeds, this technology may reduce the amount that the steering wheel must be turned (improving performance in situations such as parking and other urban area traffic maneuvers), and at higher speeds, the system helps to prevent increased steering responsiveness resulting from increased speeds (providing improved direction stability).
Adaptive steering systems may, therefore, be used to adjust a rotation angle in the steering assembly in response to a vehicle's operating conditions. For example, an adaptive steering controller may receive data regarding the vehicle's operating conditions and adjust the angle applied by the driver (i.e., the angle provided by the driver at the steering wheel). This adjustment is generally referred to as an overlay angle, and represents the difference between the angle at the steering wheel (i.e., the driver input angle) and the angle of the steered road wheels (i.e., the angle of the rod coupled to the wheels). When steering assistance degrades, however, the torque required to achieve the desired overlay angle may increase.
In vehicles with an EPAS system, the EPAS system is generally configured to continuously propagate a system status to the adaptive steering system. With this information, the adaptive steering system can properly react, for example, to a system degradation to provide an optimal overlay angle. Vehicles with hydraulic power steering systems, however, generally do not have the capability to provide feedback to the adaptive steering system regarding the system's status (e.g., that assist is limited), which may reduce the availability of the adaptive steering system (i.e., the capability of the adaptive steering system to provide the overlay angle).
It may, therefore, be advantageous to provide systems and methods that may detect the status of both types of power steering systems. It may be further advantageous to provide systems and methods that may estimate an amount of change in the steering assistance provided by such systems, and compensate for the change accordingly.